T cell responses against tumors are often directed against self-MHC molecules presenting peptides derived from over-expressed self-proteins. In general, T cells with high avidity for self-peptide/self-MHC ligands are eliminated by negative selection to prevent autoimmunity. The TCR affinity of remaining T cells specific for self-ligands is normally low, however high-avidity T cells are needed to effectively eradicate tumors. Because negative selection is limited to self-MHC molecules, T cells that recognize allogeneic MHC molecules have not undergone negative selection. Thus, if peptides are presented by allogeneic MHC molecules, it is feasible to obtain high-avidity T cells specific for common tumor-associated ligands derived from over-expressed self-proteins. T cells that recognize allogeneic MHC molecules irrespective of a specific peptide can be distinguished in vitro from allo-restricted peptide-specific T cells at the clonal level and excluded.
Significant tumor regression can occur following adoptive transfer of T cells with anti-tumor specificity. However, patient-derived T cells may have sub-optimal activity. Furthermore, T cells with appropriate specificity and function for effective tumor eradication are often not available for patients with rapidly progressing tumors. Therefore, there is current interest in using pre-characterized TCR genes to create designer lymphocytes for adoptive cell therapies. Expression of TCR-transgenes in activated lymphocytes can imbue recipient lymphocytes with anti-tumor activities comparable to the original T cells (Morris et al. Blood Rev (2006) 20, 61-69; Schumacher et al., Nat. Rev. Immunol. (2002) 2, 512-519). Moreover, some transgenic TCR can displace endogenous TCR sequences, yielding lymphocytes that express monoclonal TCR.
The first clinical trials using adoptive transfer of TCR-transgenic T cells in melanoma patients achieved clinical disease-free status in 2 of 17 patients with rapidly progressing disease (Morgan et al. Science (2006) 314, 126-129). Higher rates of clinical efficacy were obtained in patients receiving TCR transgenic lymphocytes transduced with a TCR of higher affinity but some undesired responses were noted against normal tissues. These results demonstrated the therapeutic potential of this approach however they also revealed the need to evaluate a variety of TCR sequences that recognize the same ligand but have different affinities in order to identify the most suitable TCR sequences for clinical development that can be used to achieve optimal elimination of tumor cells while showing the lowest undesired activity directed against normal, non-malignant tissues.
A number of T cell clones with specificity for various tumor-associated antigens have been reported over the years. Most of these TCR are restricted by self-MHC molecules. Further, available TCR are often of low-avidity. Multiple TCR with good capacity to recognize tumor cells via different tumor-associated antigens (TAA) are often lacking.
In the prior art, several scientific and patent documents are existing which describe TCR that are able to recognise and bind specific antigens, for example tyrosinase. Visseren et al. (Int. J. Cancer (1997) 72, 1122-1128) describe the affinity and specificity of several tyrosinase-specific TCR and suggest to use these TCR as a specific treatment of melanoma patients. Roszkowski et al. (J. Immunol. (2003) 170, 2582-2589 and Cancer Res. (2005) 65, 1570-1576) are likewise characterising tyrosinase-specific TCR.
U.S. Pat. No. 5,906,936 is directed to cytotoxic T-cells which kill non-MHC-restricted target cells independent of MHC-restriction and not to T-cells, which utilize specific TCR sequences that recognize MHC-restricted ligands.
WO97/32603 is directed to a method for producing non-human TCR and TCR specific for human HLA-restricted tumor antigens. Furthermore, the TCR-nucleic acids and recombinant T-cells are described as well as the administration of TCR recombinant T-cells for the treatment of several diseases.
WO2007/065957 describes an effector T-cell transfected with an antigen specific TCR coding RNA wherein the transfected T-cell recognizes the antigen in a complex with the MHC-molecule and binds the same. As potential tumor antigens, MART-1 (melan-A), tyrosinase and survivin are named.
WO2008/039818 discloses MART-1 and tyrosinase-specific TCR sequences and describes the enhancement of antigen recognition by substitution in the CDR2 region.
The above prior art TCR sequences are all derived from autologous or xenogeneic, but not allogeneic, sources.
For example, TCR sequences are from peripheral blood or from tumor-infiltrating lymphocytes of HLA-A2-positive melanoma patients. This means that all these TCR are HLA-A2 self-restricted TCRs, or, are HLA-DP4 self-restricted, NY-ESO-1 specific, both derived from autologous sources. As an alternative, as disclosed in WO97/32603, the TCR is derived from an HLA-A2 transgenic mouse and, therefore, the sequence is xenogeneic in this case.
However, the available prior art documents do not show TCR sequences, which are allo-restricted and specific for the survivin, tyrosinase and melan A antigens.
Thus, there is still an important need to find means to generate T cells that bear TCR with high functional avidity that have the capacity to recognize specific ligands on tumor cells.
Immune selection of tumor cells poses a severe problem in TCR-based therapies. Tumors tend to be genetically unstable and may lose their antigens by mutation. This instability may lead to the generation of antigen-loss variants which are able to escape the immune response. Therefore, if tumor cells are attacked by T cells recognizing only one single TAA specificity, this might lead to a reduced or even absent success of therapy due to outgrowth of tumor cells lacking expression of the specific TAA.
Therefore, there is a further need existing to provide a clinical approach to effectively minimize immune selection of tumor cells and to provide a broad and specific attack on tumor cells.